no oil pressure

I had the same thing happened to me when I had stamped steel rockers. Push rod went up through the rocker, push rod popped out of the lifter and the lifter popped out of the bore. BAM, no oil pressure. Like you I was on the highway (70W at the Mopar Nationals). It killed the weekend! I got the car home removed the valve cover and saw the issue. I was able to find the missing piece of the rocker and using a special tool I was able to get the lifter back into place without removing the head. I installed a new rocker and bam back in business. That is until it happened again a few months later (guess the double valve Springs didn't help). I replaced the factory setup with roller cam, lifters and rockers. No more problems.